The invention pertains to electrical units which incorporate a plurality of interconnected electrical components. More particularly, the invention pertains to electrical connection systems usable in deformable hearing aids.
Historically, hearing aids have been manufactured with a substantially rigid, non-deformable, body which incorporated a battery, an audio input transducer, a microphone, audio processing circuitry and an audio output transducer, a receiver. Conventional hearing aids of the described type have become smaller and smaller such that they are now available to be almost completely inserted into a user""s ear canal.
Interconnecting wiring in such hearing aids is very delicate given the small size of such units. The conventional types of wire known as litz wire, or magnet wire, have been chosen to reduce transmission of vibrations, mechanical energy, through the hearing aid. The transmission of mechanical vibrations within a hearing aid adds to the likelihood that the unit will oscillate and become unstable.
Hearing aids which incorporate rigid plastic housings provide physical protection for the internal wiring. That wiring does not need to be able to survive tensile loading due to deformation of the hearing aid.
As an alternate to individual wires, flex-circuits or flexible cables have been used in smaller hearing aids such as completely in-the-canal aids. The results of using flex-circuits or flexible cable have not been very satisfactory.
It has been found that vibrations will be transmitted along the circuits causing instability of performance of the respective unit. In addition, flex-circuits or flexible cables are usually designed with very specific lengths and shapes. This, as a result, is not a practical approach for custom hearing aid applications where the varying ear canal shapes which are encountered make these parameters unpredictable.
More recent technologies have focused upon compliant or deformable hearing aids. For example, elastomeric hearing aids are known which have been designed in the shape of a deformable plug. In such hearing aids, components move in different directions relative to one another. This imposes stresses on the connections. Another approach has been illustrated in Geib U.S. Pat. No. 3,527,901. Geib illustrates a resilient hearing aid housing where individual looped wires extend between processing circuitry and an output audio transducer. The looped wiring is intended to tolerate deformation of the housing wherein the output transducer moves relative to the processing circuitry. There appears to be no stress protection for the wiring.
There continues to be a need for interconnection system solutions particularly usable in deformable or compressible hearing aids. Preferably, the solution will provide increased tensile strength while not significantly increasing the mass of the respective wires. The resultant wires or cables will preferably be flexible and limp. These characteristics are especially desirable with deformable or compressible hearing aids. Such cables or wires will preferably also resist the transmission of vibrations within the respective hearing aid. Preferably such cable will protect the electronic connections in the presence of relative motion of attached electronic components.
In addition, the wiring system must be very flexible to allow the hearing aid to move or change shape in accordance with the changes in the ear canal. Stiff strain members may protect the overall hearing aid from stretching or flexing in a manner that breaks conventional wiring systems. The disadvantage of this approach is a loss in the ability of a deformable hearing aid to easily change shape. Such strain relief systems reduce the advantage of compliant hearing aids by preventing changes in the shape of the hearing aid structure.
A non-vibration transmitting wiring system incorporates a light-weight, elongated, low-mass, small cross section non-conductive and high strength strain relieving member such as a non-stretchable thread or a wire in combination with very flexible electrical wires. This strain relief member does not transmit vibrations. This member in disclosed embodiments is twisted or braided into the respective multi-conductor cable assembly.
In one embodiment, a high strength aramid-type fiber, or thread, such as KEVLAR-brand fiber, is twisted or braided with fine litz wires to create a multi-conductor cable. This cable is relatively light weight and limp enough such that it does not transmit vibrations throughout the respective hearing aid. The mechanical braiding or twisting locks the conductors and strain relief member together substantially blocking any relative movement therebetween.
Other organic fibers in the aromatic polyamide family can be used. Strong inorganic fibers can also be used.
This invention protects the wires that extend between components. Thus, components can be located in more stress prone locations (that is, in locations where more changes in shape take place).
In accordance with the invention, the elongated strain relieving members absorb the mechanical loads between respective electrical units. Light weight flexible wires such as those normally used in hearing aids provide electrical paths between the components of the respective aid but do not provide mechanical stability relative thereto. The mechanical stability is provided by the elongated strain relieving member.
In one aspect of the invention, twisted, insulated, electrical conductors and an elongated plastic strain relieving member are optionally processed so as to form a single unitary electrical cable. One form of processing is to expose or to dip the cable into a solvent, such as alcohol, which softens the external non-conductive coverings of the various conductive wires. These in turn bond to one another, and to the elongated strain relieving element, thereby creating a unitary cable. As an alternate heat, UV or RF can be used to soften the non-conductive coverings, the insulating plastic, to produce bonding between conductors. The individual wires can be coated with an adhesive, or, a UV curable plastic, which can be activated or cured after the conductors have been combined with the strain relieving member.
In yet another embodiment, the strain relief element can carry a bonding coating or adhesive. The coating or adhesive could be activated after the conductors have been combined with the strain relief member such as by ultraviolet, heat or radio frequency signals. When cured, a unitary cable structure results.
In a disclosed embodiment, the cable is subjected to five to forty twists per inch. Alternately, the wires and the elongated strain relieving member can be braided together.
The elongated strain relieving member is mechanically attached between the respective components thereby limiting movement therebetween. The conducting elements of the electrical cable can then be attached to respective contacts of the components.
The elongated strain relieving members can be attached to the respective components by adhesive, tying, trapping, or any other way that transfers the mechanical loads to the respective components. The electrical conductors themselves when attached can be longer than the length of the respective strain relieving member to permit relatively free motion between the respective components, subject to the length of the strain relieving member.
Benefits of the system of the present invention include the fact that the individual wires as well as the cables are protected from damage due to bending, and tensile forces when used in deformable or compressible hearing aids. The various disclosed cable embodiments do not contribute to vibration transmission within the respective hearing aid. Additionally, the cable subassemblies are very compatible with high quality, low defect manufacturing processes.
The invention provides wires with protection from relative movement of one component relative to another. The applied forces can be independent. The invention does not require judging from which way the force will be applied. It does not require the technician building the aid to make judgments as to which direction the components may be moving.
Numerous other advantages and feature of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings.